W204 C300 V6 CDI: power loss and jerky gear changes

[Anders]

Had my car serviced a month ago at MB, with an A0 service (incl. air filters) + gearbox oil change as the car is at 55.000 km/34000 miles.

Haven't driven the car since except this week, for a 450 km round trip. On the way down, the car was perfectly normal, back up (4 days later), the first 250 km normal, made a stop for an hour and the engine now had no power, as if the turbo did not engage and with gear changes very jerky, with down changes (e.g. Slowing down for a red light) giving a real jolt on the 2nd to 1st gear change + no kick down possible.

At some point I noticed the yellow engine management light was on (it wasn't at first) but continued to my final destination and put it in the garage. The engine, when in neutral wouldn't rev above 3000 rpm. Checking on the car 4 hours later the engine management light was still on but now it would freely rev to 4000+ rpm and power seemed to be back to normal.

Dropped it at MB this Friday, and picked it up later after I got the call that it had been repaired. The repair sheet noted a 10 kilometres road test and reprogramming the engine management. Driving off from MB it took me 500 metres to determine that the problem was still present, power down and the jolt on down changing + no kick down.

Left the car with MB, who will look at the car tomorrow, but since they have so far proved incompetent, wanted to check possible culprits with the forum experts:

- inlet manifold motor?
- sensors disturbed on the air filter change?
- insufficient gearbox fluid when they changed it?
- turbo?

Surprising/disturbing that a relatively low mileage engine, that is used exclusively for motorway driving would have what I expect to be a troublesome and costly repair...

 

[xixal]

Hi, had a similar problem recently with my MB dealer.

MB didn't until a few years ago change the ATF, it was so called sealed for life. The jerky gear change problem turned out to be insufficient oil. Some 7G gearboxes don't gave a dip stick to check the oil and this is done by heating the oil in the gearbox to certain temp and removing the filler screw, if there's too much oil it will drain until the oil reaches the overflow pipe. If there isn't enough oil it will spit a patter. Sadly even though you take your car to MB because the so called know better, the 18 year old trainee working on your car doesn't.

My car needed 2.5 litres more ATF

The engine power problems could be a number of issues. Air filter element ( MAF), faulty ignition coil, loss of turbo pressure (split pipe). STAR should have picked up some of theses issues (if they checked)

 

[Anders]

MB had the car for 3 days so far, and replaced the EGR valve yesterday to no avail, as noted by the mechanic who took the car home overnight to test this.

Still trying to diagnose but engine goes into limp mode every time it accelerates. Very rapidly losing all faith in MB and the car, but hoping for an Eureka moment.

 

[xixal]

Hi again,

Shame about the problems, if you were up my neck of the woods we could probably try a few things as I have the same car. I am finding it a little odd that STAR diagnostics isn't picking it up.

Its a long shot but some if the symptoms could relate to pressure loss within the turbo system. Remove the plastic engine cover, locate the turbo, there is a alloy pipe follow it down and it goes into flat plastic box ( believe it or not but its called a shock absorber) odd. If nothing is obvious remove the first part of the under engine cover 8 or 9 bolts (8mm) at the other end if the shock absorber you will see another large rubber pipe, make sure this is attached properly or not cracked, if its ok, check the same place on the other side of the engine, same again checking to make sure its fixed on tightly and not cracked. I have repaired several Mercs with this problem.

There are a few other things to check, but that will getting you going for now. Do it yourself, not MB dealer. Regards xixal

 

[Anders]

Got the car back this afternoon, MB decided to cover 75 % of the price of the repair, which so far only consisted of replacing the EGR valve, part number MA642 140 10 60. So far, so good. Will have another 1000 km journey Monday, guess this will be the test.

Thanks xixal for your suggestions.

 

[WG M-B]

Without fault codes its hard to give any sort of guidance. But what I will say is that without the correct torque output from the engine, the transmission will play silly buggers ( noticeable more on downshifts in lower gears )
So the transmission issues you are reporting are just software compatibility when the engine is in limp
Hope this helps